Clients can indicate on a per-connection basis that result set
metadata is optional and that the client will indicate to the
server whether to return it. Suppression of metadata transfer can
improve performance, particularly for sessions that execute many
queries that return few rows each.

There are two ways to indicate that result set metadata is
optional for a connection. They are equivalent, so either one
suffices:

At connect time, enable the
CLIENT_OPTIONAL_RESULTSET_METADATA flag for
the client_flag argument of
mysql_real_connect().

Prior to connect time, enable the
MYSQL_OPT_OPTIONAL_RESULTSET_METADATA
option for mysql_options().

For metadata-optional connections, the client sets the
resultset_metadata system
variable to control whether the server returns result set
metadata. Permitted values are FULL (return all
metadata; this is the default) and NONE (return
no metadata).

To check whether a result set has metadata, use the
mysql_result_metadata() function.
This function returns RESULTSET_METADATA_FULL
or RESULTSET_METADATA_NONE to indicate that the
result set has full metadata or no metadata, respectively.

mysql_result_metadata() can be
useful if the client does not know in advance whether a result set
has metadata. For example, if a client executes a stored procedure
that returns multiple result sets and might change the
resultset_metadata system
variable, the client can invoke
mysql_result_metadata() for each
result set to determine whether it has metadata.

For connections that are not metadata-optional, setting
resultset_metadata to
NONE produces an error.